Perfeting Mosquito Bed Net a Matter of Trial and Error

By Michelle Vachon
The Cambodia Daily 

Twenty years ago this month, a team of researchers introduced the insecticide-treated bed net for malaria control. This is the first of a three-part series on changes that its use brought to the fight against the disease.

In the early 1980s, malaria-control measures included spraying the walls of homes with insecticides, said medical entomologist Pierre Carnevale of the French Research Institute for Development. 

At the time, Carnevale was part of a research team at the Muraz Center in Burkina Faso. His team noticed that female mosquitoes which transmit malaria would 
rest on walls after biting people and be killed by the insecticide coating. 

"We thought, why not try to "intercept" them before they bite rather than after by combining bednets for physical protection with the chemical effect 
of an insecticide strong enough to stun them," Carnevale said. 

So the team, which included Yeya Toure of Mali and three other scientists from the French Research Institute Frederic Darriet, Vincent Robert, Guyen Tho Vien began testing insecticide-treated bednets in huts equipped with mosquito traps, with the support of the World Health Organization.

In July 1984, Yeya Toure presented their findings at a tropical medicine conference in Calgary, Canada. He explained that, even when using an old bednet full of holes, a treated bednet not only killed nearby mosquitoes but also served as a deterrent fewer mosquitoes entered the hut and the ones inside left quickly, 
Carnevale said. 

His team used permethrin, a type of pyrethroid insecticide first been used in agriculture in the late 1970s. 

"These were really the first class of insecticides that were considered safe to use on nets," said Jo Lines, an entomologist with the London School of Hygiene and Tropical Medecine, and the head of a British government's malaria research program. 

This product is a synthetic copy of a natural insecticide found in a flower of the chrysanthemum family, he said. 

The most commonly used type of insecticides before pyrethroids would have been too toxic to use on nets, Lines said. 

The insecticide DDT was used on nets during World War II, he said. But that product, whose use was later banned for environmental reasons, required too large a quantity per net and probably did not stick well enough, Lines said. "Pyrethroids are effective in much lower doses."

After the Calgary conference, "we swiftly went on to test nets, as you can imagine," Lines said. 

Still, it would take years of research before treated bed nets became part of malaria control programs.